In most engineered constructions, mobile or immobile, and particularly on-board of a ship, a floating construction or a non-floating off-shore construction for holding on-board human beings, one will find many pipes and/or cables extending from one compartment to another. For that purpose, floors, decks, walls or other types of partitions often comprise an opening so that the pipe and/or cable can indeed, via that opening, extend from one compartment to another. The opening may comprise a tubular passage, often referred to as a conduit. One could also consider such a conduit to be fittingly and sealingly installed into or onto the opening. Space which is in the conduit and not occupied by pipes and/or cables is usually occupied by a sealing. The purpose of the sealing is to stop undesired transport of physical phenomena through the conduit. For instance, the sealing may be designed to stop the flow of air, water, noise, fire, poisonous gases, smoke, etc., dampen noise and vibrations, and keep a fire for as long as possible isolated on one side of the conduit without spreading via the conduit to another compartment. The sealing systems are tested before they are put on the market so as to be able to assess their performance under exposure to predefined circumstances. Accordingly, sealing systems may be certified. For instance, a certificate may be issued for remaining intact under exposure to a nearby fire for the time of one hour. The number of pipes and/or cables extending through the conduit, the type of sealing applied, the temperatures exposed to, etc. are recorded on or with the certificate. The availability of these certificates facilitates choosing a particular sealing system for use, particularly on-board at a specific location for conduits through which a certain number of pipes and/or cables extend.
A number of sealing systems are known in the marketplace. One system is often referred to as the “block system”. It was, for instance, installed on the Emma Maersk which according to the official accident report got flooded in the Suez Canal in February 2013 and almost sunk, partly due to a failure of the block system. The system comprises modular rubber blocks for placement in a conduit. A number of the blocks are provided with a hole for holding a cable. The blocks are built up from two half blocks, each having a recess that forms half the hole. There may also be wedge blocks, sometimes provided with bolts; there may be modular blocks without a hole for occupying surplus space in the conduit, and stay plates. The conduit may comprise a welded frame. In use, a number of cables of different diameters may extend through the conduit. Then, the conduit contains the modular blocks (the blocks with a hole for a cable and the blocks without such a hole). The wedged blocks are normally put between these modular blocks with the aim to make the construction of the modular blocks tight and firm. The stay plates are fitted with layers of these blocks and aim to keep these blocks in the right position in the welded frame. A mechanism may be available for putting the blocks under pressure aimed at tightening sealing by the blocks. Such mechanisms are often referred to as compression units. As explained in the accident report, the system failed on at least an individual component level.
With the block system, there is a need to compress the blocks after positioning in the welded frame, i.e. the conduit. Compressing the components will, in the long run, result in deterioration of these components, due to time-related phenomena like creep and stress relaxation. Deterioration not only occurs on the level of the components, but also on the level of the sheathing of the cables. These can be irreversibly deformed by the applied compression of the blocks surrounding a cable. As a result of this, replacing an existing sealing system by a similar sealing system comprising blocks having a hole, is highly unlikely to work well as the diameter of the cable may have changed.
In this context, reference is also made to IEC 60079-14, particularly clause 9.1.4 which indicates that “low smoke and/or fire resistant cables usually exhibit cold flow characteristics”. This seems to be particularly relevant for thermoplastic materials which tend to flow when subjected to pressure at ambient temperature.
Given that certificates are issued on the basis of tests for which normally a brand new sealing system is applied, and as explained above a sealing system known in the marketplace deteriorates after installation over time, there is a need for (re-)sealing existing conduits through which a number of cables extend.
One way of re-sealing an existing conduit through which a number of cables extend would be to remove the existing sealing system, if possible, and then to install a system that is known to more reliably provide a sealing integrity over a long period of time, preferably without any need for maintenance or re-tightening. However, this would be a very costly event as it would entail very carefully removing the sealing system so as not to damage the cables and their present position. However, given that the present sealing system, as explained above, applies a pressure onto the sheathing of the cables extending through the conduit, uncontrolled deformation of the sheathing may have taken place. As a consequence thereof, there is no longer a well-defined diameter of the cables within the conduit, so that it is difficult to apply a new sealing system that would require accurate knowledge of the diameters of the cables in the conduit. Most importantly though, removing the existing sealing, or elements which hold the cables in position in the conduit, would be extremely time-consuming and lead to lengthy downtime of the engineered construction in which the conduit is present.